MRAM with means of controlling magnetic anisotropy

Abstract

We describe the manufacturing process for and structure of a CPP MTJ MRAM unit cell that utilizes transfer of spin angular momentum as a mechanism for changing the magnetic moment direction of a free layer. The strength of the switching field, Hs of the cell is controlled by the magnetic anisotropy of the cell which, in turn, is controlled by a combination of the shape anisotropy and the stress and magnetostriction of the cell free layer. The coefficient of magnetostriction of the free layer can be adjusted by methods such as adding Nb or Hf to alloys of Ni, Fe, Co and B or by forming the free layer as a lamination of layers having different values of their coefficients of magnetostriction. Thus, by tuning the coefficient of magnetostriction of the cell free layer it is possible to produce a switching field of sufficient magnitude to render the cell thermally stable while maintaining a desirable switching current.

Description

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] This invention relates generally to a current perpendicular to plane random access memory (CPP-MRAM) cell formed as a magnetic tunneling junction (MTJ) using a spin transfer effect to change the magnetization of a free layer.

[0003] 2. Description of the Related Art

[0004] The conventional magnetic tunneling junction (MTJ) device is a form of ultra-high magnetoresistive (MR) device in which the relative orientation of the magnetic moments of parallel, vertically separated magnetized layers, controls the flow of spin-polarized electrons tunneling through a very thin dielectric layer (the tunneling barrier layer) formed between those layers. When injected electrons pass through the upper layer they are spin polarized by interaction with the magnetic moment of that layer. The majority of the electrons emerge polarized in the direction of the magnetic moment of the upper layer, the minority being polarized opposite to that dire...

Examples

Embodiment Construction

[0037]The preferred embodiment of the present invention is an MRAM cell of the spin-transfer variety, having a CPP-MTJ configuration and including a free layer whose switching field, Hs is a result of a magnetic anisotropy produced by a combination of shape anisotropy and stress-induced magnetostriction. The pinned layer can be a single layer of ferromagnetic material or a synthetic (SyAP) antiferromagnetic layer. As noted above, during operation of the cell, the passage of a current perpendicularly through the free layer produces a torque induced switching of the free layer magnetization due to the interaction of the spins of the conduction electrons with the magnetic moment of the free layer. The torque must be sufficient to switch the magnetization direction, against the countering effect of the switching field. Once the switch is complete, the same switching field provides sufficient magnetic energy to the magnetic moment configuration to stabilize the magnetization against ther...

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] This invention relates generally to a current perpendicular to plane random access memory (CPP-MRAM) cell formed as a magnetic tunneling junction (MTJ) using a spin transfer effect to change the magnetization of a free layer.

[0003] 2. Description of the Related Art

[0004] The conventional magnetic tunneling junction (MTJ) device is a form of ultra-high magnetoresistive (MR) device in which the relative orientation of the magnetic moments of parallel, vertically separated magnetized layers, controls the flow of spin-polarized electrons tunneling through a very thin dielectric layer (the tunneling barrier layer) formed between those layers. When injected electrons pass through the upper layer they are spin polarized by interaction with the magnetic moment of that layer. The majority of the electrons emerge polarized in the direction of the magnetic moment of the upper layer, the minority being polarized opposite to that dire...

Examples

Embodiment Construction

[0037]The preferred embodiment of the present invention is an MRAM cell of the spin-transfer variety, having a CPP-MTJ configuration and including a free layer whose switching field, Hs is a result of a magnetic anisotropy produced by a combination of shape anisotropy and stress-induced magnetostriction. The pinned layer can be a single layer of ferromagnetic material or a synthetic (SyAP) antiferromagnetic layer. As noted above, during operation of the cell, the passage of a current perpendicularly through the free layer produces a torque induced switching of the free layer magnetization due to the interaction of the spins of the conduction electrons with the magnetic moment of the free layer. The torque must be sufficient to switch the magnetization direction, against the countering effect of the switching field. Once the switch is complete, the same switching field provides sufficient magnetic energy to the magnetic moment configuration to stabilize the magnetization against ther...

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